Conversion of hydrocarbons



Filed Sept. 28, 1942 NNN,

tba

Patented June 12, 1945 CONVERSION HYDROCABBQNS Vladimir Haensel andBernard S. Friedman, Chicago, Ill., assignors to Universal Oil ProductsCompany, Chicago, Ill., a corporation of Dela- Wale ApplicationSeptember 28, 1942, Serial No. 459,939

11 Claims.

This invention relates to the conversion of hydrocarbons and moreparticularly to va combination oi interdependent and cooperative stepswhereby a hydrocarbon mixture comprising essentially parafllns andoleilns is separated into a second mixture of isoparafflns and oleilnsand this second mixture is subjected to alkylation to produce asaturated high antiknock distillate. This distillate is substantiallysaturated in character and is of high antiknock value. The major portionof this distillate boils within the range of gasoline and isparticularly suitable for use in aviation gasoline.

In the alkylation of isoparamns by olens, it is essential that an excessof isoparafiins be present in the reaction zone in order to minimizeundesirable polymerization reactions and also because the presence of anexcess of isoparaillns has been found to yield alkylation products o fhigher antilmock properties. The ratio of isoparamns to olefins isusually within the range of 3:1 to as high as 20:1 or, in certain cases,even higher. l

In addition, experiments have shown that the presence of substantialamounts of normal paraillns in the alkylation zone has a deleteriouseilect upon the alkylation reaction. Further, the presence of such largeamounts of normal parafflns increases the size of the alkylationequipment and thus adds considerably to the cost of alkylation plants.Also, this presence of large quantities of normal paraiiins in thealkylation zone creates a heavy burden on the subsequent fractionationequipment of the process. In the alkylation processes heretoforeproposed, the products from the alkylatlon zone comprise principallyalkylate, normal parains and excess isoparaiilns, and entailsfractionation and distillation equipment of considerable expense inorder to eect separation of these products. It is a particular featureof'the present invention that this excessive cost of fractionation isgreatly reduced by the combination of interdependent steps disclosedherein.

According to the present invention, the charging stock, comprisingessentially a mixture of oletlns and paraiilns, is subjected toextraction in the presence of a particular separating agent which hasbeen found to have a high capacity, that is, it will dissolve largeproportions of the hydrocarbons and, in addition,.it has a highselectivity-that is, it will dissolve the oleiins preferentially totheparafilns. The extract phase, comprising principally the olens andseparating agent, is subjected to treatment with an isopar- (Cl.26o-683.4)

aln in order to release the oleilns and to thereby produce a mixtureoi.' isoparaiiin and oleflns for the subsequent alkylation step of theprocess. Another particular feature of the present invention is that thequantity of oleflns absorbed by the separating agent and the oleflnsreleased by contact with the isoparaiilns are balanced to produce anisoparailin-oleiln mixture of the correct composition required foroptimum alkylation. 'I'hese results are achieved by the use of theparticular separating agent and the particular combination ofinterdependent steps disclosed herein.

In one specific embodiment the present invention comprises subjecting anolen-parafln mixture to extraction with a separating agent comprisingessentially a phosphoric acid solution of silver phosphate, separatingan extract phase from a' raillnate phase, contacting the extract phasewith an isoparamn in order to separate an isoparain-oleiin mixture inwhich the ratio of isoparamns to olefin is within the range of 3:1 to:1, subjecting said isoparailin-olefln mixture .to alkylation in thepresence of an alkylation catalyst,vfractionating the products of saidalkylation to separate afraction comprising principally isobutane andrecycling said fraction to the process.

'Ihe invention will be further explained in connection withtheaccompanying drawing which 30 illustrates a ilow diagram of onemethod in which the process may be conducted. However, it is notintended to limit the invention to the particular flow as shown in thedrawing.

In order to simplify the further explanation of the invention thefollowing description will be limited to the treatment of abutane-butylene charging stock. The butane-butylene fraction charged tothe process will usually vary in its composition of normal butane,isobutane, normal butylene and isobutylene, as well as in the minorquantities of the lower and high boiling compounds, depending upon thesource from which it is obtained and upon the method by which it isrecovered. It is understood that the invention is not limited to thetreatment of butane-butylene mixtures but that the invention isapplicable to the treatment of other mixtures containing olens andparail'lns which are suitable, after treatment in the early stages ofthe present combination process, for alkylation in the subsequent stageof the process. Y

Ii the charging stock contains'suliur or sulfur compounds, the chargingstock is preferably given a preliminary treatment in order to remove the56 sulfur therefrom. Usually a caustic wash will be sumcient to removethe hydrogen sulfide but, if necessary, a. more severe treatment may beemployed.

Referring' to the drawing, the charging stock is introduced to theprocess through line I and is directed into primary extractor or zone 2,which may be of any suitable type in order to effect the desired contactof the charge with the separating agent. Thus. this zone may take theform of one or more zones which may or may not contain packing materialsuch as gravel, clay, synthetically prepared composites, etc., and/orfractionating means such as baille plates, bubble trays or the like. Inthe particular case illustrated in the drawing, countercurrent flow of.hydrocarbons and separating agent is shown, although it is understoodthat concurrent flow may also be utilized.

Referring again to the drawing, the separating agent may be introducedthrough line 3 to zone 2 and, after the operation of the process hascommenced, the separating agent may comprise all or a portion thereofwhich is recycled within the process in a manner to be hereinafterdescribed in detail.

The separating agent of the present invention comprises a phosphoricacid solution of silver phosphate. Experiments indicate the best resultsare obtained when employing high concentrations of silver phosphate.However, the concentration of the silver phosphate is limited by theconcentration of the phosphoric acid. On the other hand, theconcentration of the phosphoric acid is limited since the undiluted acidis too viscous and also since the undiluted acid tends to catalyzeundesired reactions. Thus. for example, it has been found thatphosphoric acid solutions of greater than 95 percent concentration aretoo viscous for practical use at ordinary temperatures. Therefore,according to the present invention, the phosphoric acid solution shouldbe below 95 percent concentration and preferably below 90 percentconcentration.

Effective separating agents have been prepared comprising 30 percentsilver phosphate and 70 percent by weight of phosphoric. acid of 85percent concentration. Likewise, effective separating agents have beenprepared comprising 18 percent silver phosphate and 82 percent by weightof phosphoric acid. of 67.5 percent concentration. In general, it ispreferred to utilize as high a concentration of the acid as issatisfactory in connection with the particular separation desired andalso to use as high a concentration of the silver phosphate as may bedissolved therein. In most cases the concentration of phosphoric acidshould be above 50 percent.

'I'he silver phosphate-phosphoric acid solution may be prepared in anysuitable manner. One convenient method is to mix the required amount ofsilver phosphate in a concentrated phosphoric acid solution and then addthe necessary amount of water in order to yield a separating agent ofthe desired concentration. On the other hand the phosphoric acid may bediluted prior to the addition of the silver phosphate.

The temperature employed in primary extractor 2 will depend upon theparticular compounds being treated and may range from subatmospheric upto 150 F., or more. In general the temperature should be below 150 F.,in order to avoid undesired reactions which will occur at the highertemperatures. Although atmospheric, subatmospheric or superatmosphericpressures may be employed, it is generally preferred to employ sumcientsuperatmospheric pressure in order to maintain the hydrocarbons insubstantially liquid phase.

The hydrocarbons and separatingagent are then allowed to settle ineither extractor 2 or in other zones into an extract phase and araillnate phase. In multiple stage operations, the railinate phase maybe contacted with further quantities of the separating agent in order tofinally recover substantially all ofthe oleiins contained in thecharging stock. The extract phases may then be combined and directedthrough line l into secondary extractor 5.

The raffinate phase or phases may be withdrawn from the upper portion ofextractor 2 through line 6 and treated to separate the separating agentfrom the hydrocarbons. This may take any convenient form and theseparating agent may be recycled, by well-known means not illustrated,to the extract step of the process. The saturated hydrocarbons are thendirected into isobutane column 1 wherein they are fractionated in orderto separate isobutane from normal butane. 'I'he normal butane is removedthrough line 8 to storage or any desired further treatment or use. Theisobutane is removed through line 8 and a portion thereof may bewithdrawn from the process. while all or at least the remaining portionis directed through line l0 into secondary extractor 5. Line Il isprovided for the introduction of additional isobutane, if required.

Secondary extractor 5 is usually operated within the same range ofconditions heretofore specii'led in connection with primary extractor 2,that is, temperatures of below about F., and sumcient superatmosphericpressure to maintain the hydrocarbons in substantially liquid phase. Itis believed that a complex is formed between the olens and theseparating agent and that this complex is in equilibrium in the extractphase. By contacting the isoparafns with the extract phase, thisequilibrium is disturbed and the oleiins are released. from the solutionin order to maintain the new equilibrium established. Thus, a veryeiective and ready separation of the oleiins is accomplished in animproved manner.

The use of isobutane or other isoparains which are to be subsequentlyalkylated as the stripping medium in this step of the process, is ofprime importance since it eliminates any further fractionation of themixture of isoparaiiin and olefin, and this is one of the particularfeatures of the present invention.

Another important advantage of this method of operation is that iteliminates the necessity of heating the extract phase to hightemperatures in order/to separate the oleflns. Heating to hightemperatures may cause polymerization or hydration reactions which areundesired in the particular process of the present invention.

The silver phosphate-phosphoric acid solution is removed from extractor5 through line l2 and all or a portion thereof may be withdrawn from theprocess. Preferably, however, the greater portion of this solution isrecycled by way of lines I2, I3 and 3 to extractor 2 for further use inthe process.

The isobutane-olen mixture is withdrawn through line il from the upperportion of extractor 5 and, as a particular feature of the presentinvention, .this stream has a composition of isoparafn to olefin withinthe range of 3:1 to 20:1 and in most cases the ratio. of isoparaiiin .toolen will be within the range of 5:1 to 10:1.

,avaaie This stream is then directed through line Il into alkylationzone II.

Alwlation zone il may comprise any of the well-known forms oi'alkylation equipment suitable for obtaining intimate contact between thehydrocarbon reactants and the alkylation catalyst under controlledconditions of temperature,

`pressure and time of contact. Any suitable alkylatlon catalyst may beemployed, the preferred catalysts being hydrogen fluoride, sulfuric acidand phosphoric acid, although these catalysts are not necessarilyequivalent in their activity in eiecting the desired reaction. Undercertain circumstances, metal halides and particularly aluminum chloridemay be utilized as the catalyst. The present invention is not limited toany particular catalyst and, even in certain cases. where it is desiredto effect the reaction by purely thermal means. the catalyst may beomitted. Although not illustrated in the drawing, when a mineral acidcatalyst in liquid condition is employed, suitable means will, ofcourse, be provided for the introduction and withdrawal of the catalyst.Likewise, it is within the scope of the invention to recycle all or aportion of the catalyst within the alkylation zone or to regenerate thecatalyst prior to such recycle.

The exactftemperature and pressure to be employed in the alkylationreaction will, of course, depend upon the catalyst. When utilizinghydrogen fluoride catalysts, the temperatures employed are usuallywithin the range of about 50 F., to about 200 F., and preferably betweenabout 60 F., to about 125 F. Usually sufilcient pressure is employed tomaintain the reactants in liquid phase, although it is within the scopeof the invention to utilize .vapor or. mixed phase operations whendesired.

The alkylation products are directed through line I 8 into debutanizingcolumn I1. As a particular feature of the present invention, theproducts being introduced into zone I1 will comprise principallyalkylate and excess isobutane. Thus, a simple debutanizing operationwill effect the desired operation in order to evolve and remove theisobutane from the liquid alkylate. In contrast, in the absence of thefeatures ofthe present invention, the products from the usual alkylationprocess contains varying proportions of normal butane in addition to theisobutane and alkylate. This then requires rather expensivefractionating equipment for accomplishing the desired separation.

The liquid alkylate is withdrawn from zone I1 through line 'I8 andusually will be rerun in a separate zone to eiect the recovering ofgasoline or gasoline fractions of the desired end boiling point. f

The separated isobutane is withdrawn from the upper portion of the zoneI'I and all or a portion thereof may be removed from lthe processthrough line I9. Preferably, however, at least a. portion of theisobutane will be recycled to the alkylation step by way of lines and 2I. In case other components are present in suilcient quantity in theisobutane stream withdrawn from zone I1, it is within the scope of theinvention to direct all or a portion of this stream through lines 22 and8 into isobutane column 1. Likewise, when desired, all or a portion ofthe isobutane stream may be directed through lines 20 and I0 tosecondary extractor 5.

The following example is vintroduced for the purpose of furtherillustrating the nature of the invention and is not intended to undulylimit A butene-butylene fraction containing 20 percent of butylenes issubjected to extraction at a temperature of about 100 F.,- with aseparating agent comprising 30 percent by weight of silver phosphate and70 percent by weight of 85 percent phosphoric acid. The extract phase isthen contacted with isobutane suiilcient to separate most of thedissolved olefin and to yield an iscparailin-oleiln mixture in which theratio of isobutane to oleiln is 10: 1. The isoparafhn-olefin mixture-isthen subjected to alkylation at a temperature of abou-t 100 F., in thepresence of hydrogen fluoride catalyst. The products are fractionated toseparate alkylate from isobutane, a portion of 'the isobutane beingrecycled to the isobutane column and the remaining portion beingsupplied to the secondary extractor. The alkylate is furtherfractionated to separate a fraction having a 300 F., end boiling pointand this latter fraction is of high antiknock value nd particularlysuitable for use in 'aviationgaso- We claim as our invention:

1. A process for preparing an isoparailln-olerln fraction relativelyfree "of normal paraffin, which comprises contacting a hydrocarbonfraction containing olens and normal and isoparaiilns with a phosphoricacid solution of silver phosphate under conditions such that there isformed an olefin extract phase containing said solution and said olensin the proportion at least approaching that of an equilibrium mixture ofthe two components, separating the extract phase from the parailln orramnate phase and contacting an isoparamn with said extract phase underconditions such that equilibrium in the extract phase is disturbed andthe olens released therefrom.

2. The process defined in claim 1 further characterized in that theamount oi' isoparailln con- 40 tacted with said extract phase is inexcess of the raflinate phase into a normal parafnn part and anisoparailin part and contacting an isoparaln including the isoparaillnseparated from the ramnate phase with said extract phase underconditions such that equilibrium in the extract phase is disturbed andthe olei'ins released therefrom.

4. A process for preparing an isobutane-butene fraction relatively freeof normal butane which comprises contacting a C4 hydrocarbon fractioncontaining butenes and normal and isobutanes with a phosphoric acidsolution of silver phosphate under conditions such that there is formeda butene extract phase containing said solution and said butenes in theproportion at least approaching that of an equilibrium mixture of thetwo components. separating the extract phase comprises contacting a C4hydrocarbon fraction containing butenes and normal and iscbutanes with aphosphoric acid solution oi.' silver pliesphate under conditions suchthat there is formed a butene extract phase containing said solution andsaid butenes in the proportion at least ap-` proaching that of anequilibrium mixture of the two components, separating the extract phasefrom the butane or ramnate phase, separating said rafiinate phase into anormal butane part and an isobutane part and contacting isobutaneincluding that separated from said ramnate phase with said extract phaseunder conditions such that equilibrium in the extract phase is disturbedand the olefins released therefrom.`

6. The process deilned in claim 5 further characterized in that theamount of isobutane contacted with said extract phase is in excess oi.'the amount of normal and isobutane in said C4 fraction.

7. A process for preparing an isobutane-butene fraction relatively freeof normal butane, which comprises contacting a C4 hydrocarbon fractioncontaining butenes and normal and isobutanes with a phosphoric acidsolution of silver phosphate, at a temperature below about 150 F. andunder a superatmospheric pressure sumcient to maintain the C4hydrocarbons in substantially liquid phase, thereby forming an extractphase containing butenes and said solution in the proportion at leastapproaching that of an equilibrium mixture of the two components,separating the extract phase from the butane or raiiinate phase,separating said raillnate phase into a normal butane part and anisobutane part and extracting the butenes from said extract phase at atemperature below about 150 F. by contacting therewith isobutaneincluding isobutane from said raflinate phase, in suillcient amount todisturb the equilibrium in the extract phase and release the butenestherefrom.

8. A process which comprises contacting a C4 hydrocarbon fractioncontaining butenes and normal and isobutanes with a phosphoric acidsolution o! silver phosphate under conditions such that there is formeda butene extract phase conavaria taining said solution and said butenesin the proportion at least approaching that of an equilibrium mixture ofthe two components, separating the extract phase fromV the butane orraiiinate phase, stripping the butenes from said extract phase bycontacting therewith isobutane includlng that separated from saidrailinate phase in an amount suillcient to disturb the equilibrium inthe extract phase and release the butenes therefrom, subjecting theresultant isobutanebutene traction to alkylation in the presence of analkylating catalyst different in composition than the silver phosphatesolution, separating unreacted isobutane from the products of alkylationand returning the isobutane thus separated t0 the olefin stripping step.

9. A process for preparing an isoparailn-olen fraction relatively freeof normal parailln which comprises contacting a. hydrocarbon fractioncontaining oleiins and normal and isoparaiiins with a phosphoric acidsolution of silver phosphate under conditions such that oleiins areabsorbed in the extract phase, separating the resultant extract phasefrom the raflinite phase and contacting an isoparaiiin fractionrelatively free of normal paraiiins with said extract phase to extractoleiins from the latter.

10.- A process for preparing an isoparain-olen fraction relatively freeof normal paraffin which comprises contacting a hydrocarbon fractioncontaining olens and normal andisoparains with a phosphoric acidsolution ot silver phosphate under conditions such that olens areabsorbed l VLADIMIR. HAENSEL. BERNARD S. FRIEDMAN.

